In order to reduce the generation of manmade greenhouse gases and also considering the depletion of conventional sources of energy like coal and oil, more and more green energy technologies had been developed and among which solar power is considered to be one of the most promising renewable energy sources in the world. However, since the thin film crystalline silicon solar cell that are currently available are still poor in performance efficiency and are very expensive to built, each unit of electricity cost from solar power is higher than those of conventional thermal power plants and nuclear power plants, so that solar power is not yet being used as our main source of electricity. The best way for making solar cells to become more popular is to improve the solar cell's efficiency for lowering power generation cost without causing any increment in its manufacturing cost and complexity, which is becoming the focus point in the recent thin film solar cell (TFSC) development for achieving a novel thin film solar cell with low material requirement. In order to effectively enhancing the internal quantum efficiency and the absorption of solar spectrum, a light trapping structure with specific diffusion characteristic had been studied and provided, using which the light incident to a thin film solar cell at critical angles is refracted and reflected multiple times for greatly increasing the probability of absorption, and thus the energy conversion efficiency of the thin film solar cell is improved.
Nevertheless, it is known that almost all the technologies and related manufacturing processes of thin film solar cell with light trapping structure are already being thoroughly studied and developed by those advanced countries, not to mention the related studies in light trapping based on nanoengineering. Therefore it can be very costly for those new corners to the solar cell industry since they are going to face very high royalty payments and may even fall into “the money pit game”, such as what was happening to the TFT LCD and DRAM industries in Taiwan. Hence, it is important for those new corners to develop its own novel manufacturing processes with reduced cost.
There are already all kinds of light trapping structures available on the market. One of which is a submicrometer grating, that is to be formed on a back surface reflector of a solar cell and used for increasing the optically effective cell thickness by approximately a factor of 5. However, such submicrometer grating is difficult to fabricate, not to mention the fabricating of a large-area submicrometer grating. In 1998, a novel porous silicon backside light reflector for thin silicon solar cells was provided by Zettner et al., using which the photoelectric current from the solar cell is increased by about 20%. However, to produce such porous reflector on solar cell effectively will require a process with very precise parameter control. Moreover, another conventional light trapping structure is achieved by texturing the incident surface of silicon solar cells, in that the textured surface is formed on the incident surface of a solar cell by a lithography process, a dry-etching process, or a wet-etching process. However, the forming of the textured surface by the lithography process is disadvantageous in that: not only the equipment for those production processes can be very expensive as the equipment should be large enough for producing large-area textured surfaces, but also the performing of those production processes can be very time-consuming and costly. Thus, it is in need of a novel light trapping structure without the aforesaid shortcomings.